Binary Offset Carrier Signals Research Articles

Research on a High-Dynamics Acquisition Algorithm for New Binary Offset Carrier Signal in UAV Communication

As unmanned aerial vehicles (UAVs) are widely used in various fields, there is an increasing demand for UAV anti-jamming, multipath mitigation, and covert secrecy. Frequency-hopping binary offset carrier (FH-BOC) signals possess higher anti-jamming and multipath mitigation capabilities than direct-sequence spread spectrum (DSSS) and binary offset carrier (BOC) signals. A prerequisite for constructing communication links between UAVs using FH-BOC signals is the design of efficient acquisition algorithms to capture the signals successfully. In this paper, the modulation and characteristics of the FH-BOC signal are introduced. The maximum relative velocity between UAVs is 5.5 km/s, the maximum acceleration is 50 g, and the maximum plus acceleration is 20 g/s. In this high dynamic environment, the parameters for the parallel code phase and Partial Matched Filter–Fast Fourier Transform (PMF-FFT) acquisition algorithms targeting FH-BOC(10,1) signals are designed, and the acquisition performance of these algorithms is comparatively analyzed. The acquisition time for the first and second algorithms is 4.3317 s and 6.137 s. The number of real additions required by the first and second algorithms is approximately 10.9×109 and 8.9×109, and the number of real multiplications is approximately 7.6×109 and 6.7×109. This helps in selecting the acquisition algorithm when FH-BOC signals are used to build inter-UAV communication links.

A Cumulant-Based Method for Acquiring GNSS Signals.

Global Navigation Satellite Systems (GNSS) provide positioning, velocity, and time services for civilian applications. A critical step in the positioning process is the acquisition of visible satellites in the sky. Modern GNSS systems, such as Galileo-developed and maintained by the European Union-utilize a new modulation technique known as Binary Offset Carrier (BOC). However, BOC signals introduce multiple side-peaks in their autocorrelation function, which can lead to significant errors during the acquisition process. In this paper, we propose a novel acquisition method based on higher-order cumulants that effectively eliminates these side-peaks. This method is capable of simultaneously acquiring both conventional ranging signals, such as GPS C/A code, and BOC-modulated signals. The effectiveness of the proposed method is demonstrated through the acquisition of simulated signals, with a comparison to traditional methods. Additionally, we apply the proposed method to real satellite signals to further validate its performance. Our results show that the proposed method successfully suppresses side-peaks, improves acquisition accuracy in weak signal environments, and demonstrates potential for indoor GNSS applications. The study concludes that while the method may increase computational load, its performance in challenging conditions makes it a promising approach for future GNSS receiver designs.

Binary Offset Carrier (BOC) and Binary Phase Shift Keying (BPSK) Modulation in Indoor Drones GNSS Recievers using Multipath Error Envelope MEE Technique

The applications of unmanned aerial vehicles (UAVs) have greatly eased the lives of human being. Due to the mass commerial production of UAVs (or Drones) and the support of the ongoing scientific research, it can now be used in disaster monitoring, surviellance, fire conrolling and many outdoor usages. However, the indoor applications have stricter requirements for the autonomous positioning capability of UAVs, requiring its positioning accuracy to be within the narrower areas and aisles. The Global Navigation Satellite System (GNSS) is currently the only guidance and autorecovery method that can be applied directly and consistently to UAV positioning. The current GPS L1C and/or Galileo E1 open services signals are being widely used for this purpose. Moreover, the Binary Offset Carrier (BOC) techniques have been recently adopted in Galileo and GPS BIII as one of the efficient mitigation methods to decrease the interference/multipath delays and to increase both the Position Accuracy and the immunity of GNSS interferences. This research aims to present a software method of assessing the improvements of the Accuracy, and yet the Availability, by producing the MEE for BOC technique. The used methodology is analyzing the theoretical equations behind the interfernece multipath error envelopes in both BPSK and the new BOC signals. The Results show a higher performance of BOC GNSS Recievers over BPSK ones, and less delay.

Enhanced Synchronization Algorithms for BOC Signals Based on Reconstructed Sub-Correlation Functions

Aiming at the ambiguous synchronization of binary offset carrier (BOC) and composite binary offset carrier (CBOC) modulation signals due to secondary peaks for Global Navigation Satellite System (GNSS), a reconstructed sub-correlation function synchronization algorithm (RSSA) for BOC and CBOC is proposed. The general autocorrelation subfunctions of BOC and CBOC are obtained by deriving the subfunctions of the cross-correlation function between BOC signals with different modulation orders. According to the characteristics of the subfunctions, the corresponding reconstruction rules are set to obtain the unambiguous correlation functions. To further reduce the complexity of the local auxiliary signal, a local auxiliary signal optimization algorithm (LASOA) is proposed based on RSSA, which only needs to generate a local two-level signal compared to the conventional CBOC local four-level signal. The simulations show that the two algorithms proposed in this paper reduce the amplitude of the side peaks of the normalized correlation peaks of BOC by at least 0.09 compared with the autocorrelation side-peak cancellation technique (ASPeCT), maintain a high detection probability, and the multipath error is smaller than that of the autocorrelation side-peak cancellation technique (ASPeCT) and other traditional algorithms. The phase discrimination curves show that the linear region slope gains of the two algorithms in this paper are above 2 dB compared with the ASPeCT and other conventional algorithms.

A Novel Unambiguous Acquisition Algorithm Based on Segmentation Reconstruction for BOC(n,n) Signal

In order to improve the frequency band utilization and avoid mutual interference between signals, the BD3 satellite signals adopt Binary Offset Carrier (BOC) modulation. On one hand, BOC modulation has a narrow main peak width and strong anti-interference ability; on the other hand, the phenomenon of false acquisition locking caused by the multi-peak characteristic of BOC modulation itself needs to be resolved. In this context, this paper proposes a new BOC(n,n) unambiguous acquisition algorithm based on segmentation reconstruction. The algorithm is based on splitting the local BOC signal into four parts in each subcarrier period. The branch signal and the received signal are correlated with the received signal to generate four branch correlation signals. After a series of combined reconstructions, the final signal detection function completely eliminates secondary peaks. A simulation shows that the algorithm can completely eliminate the sub-peak interference for the BOC signals modulated by subcarriers with different phase. The characteristics of narrow correlation peak are retained. Experiments show that the proposed algorithm has superior performance in detection probability and peak-to-average ratio.

Multipath Mitigation for BOC Signals Based on Prompt-Assisted-Offset Correlator

Tracking ambiguity and multipath are two serious threats in processing binary offset carrier (BOC) signals that are widely used in global navigation satellite systems (GNSS). Three-loop tracking methods, such as dual binary phase-shift keying tracking (DBT), use a delay lock loop (DLL), a phase lock loop (PLL), and a subcarrier PLL (SPLL) to track the code, carrier, and subcarrier, respectively, thus solving the tracking ambiguity problem. However, the multipath remains an important factor in the ranging performance deterioration of these tracking methods. Using the offset correlator (OC) technique in the SPLL can effectively mitigate subcarrier multipath errors, but it substantially raises thermal noise errors. To solve this contradiction, this paper proposes a prompt-assisted-offset correlator (PAOC) technique that combines the prompt and offset correlators in a complementary way to mitigate multipath for BOC signals. Compared with the original OC technique, the PAOC technique has less thermal noise performance loss. Moreover, this paper discovers and quantifies the interaction between carrier and subcarrier multipath errors by analyzing the coupling effect between SPLL and PLL. Most multipath mitigation methods for BOC signals ignore the carrier multipath in the PLL, so their subcarrier multipath performance is not optimal. Thus, this paper further proposes applying the PAOC technique in both PLL and SPLL to mitigate carrier and subcarrier multipath errors simultaneously. Theoretical analysis and experimental results demonstrate that the proposed method can significantly improve the multipath performance with small noise performance loss.

Dual High Resolution Correlators for Multipath Mitigation in BOC Signals

Multipath is a dominant source of positioning errors in global navigation satellite system receivers. It is difficult to design multipath mitigation techniques for binary offset carrier (BOC) signals due to the complicated autocorrelation function of BOC signals and localized variations of multipath. In this paper, a dual high resolution correlators (DHRC) technique is proposed for BOC signals to mitigate code and subcarrier multipath errors, as well as the carrier multipath error that is neglected by common techniques. Based on the concept of dual binary phase-shift keying (BPSK) tracking, the BOC signal is decomposed into two BPSK signals located in the upper and lower sidebands, respectively, thereby transforming the multipath mitigation in the BOC signal into the multipath mitigation in the upper and lower sidebands. Two narrow correlation functions of the upper and lower sidebands are synthesized using multiple correlation values, so the multipath outside the main peak of the synthesized correlation function is eliminated. The peak value of the synthesized correlation function is reduced from the original ACF, resulting in a large noise error. Therefore, a complementary filter is designed to compensate the noise error. Theoretical analysis and simulation results demonstrate that the DHRC technique with complementary filters can significantly mitigate multipath errors for BOC signals with slight thermal noise performance loss.

Integrated Communication and Measurement System with BOC-Assisted OFDM

For unmanned aerial vehicles (UAVs), high-precision measurement and high-speed communication are necessary to realize flight and operational missions. In this paper, we propose an integrated communication and measurement system in a Doppler frequency offset environment. The system combines orthogonal frequency division multiplexing (OFDM) modulation with binary offset carrier (BOC) modulation to formulate an OFDM+BOC composite signal through power control. High-precision measurement is achieved through BOC modulation, and high data transmission is achieved through OFDM modulation. Furthermore, the high-precision Doppler frequency offset tracked by the BOC signal is adopted to assist in the demodulation of the OFDM signal. This substantially decreases the impact of the Doppler frequency offset on the OFDM signal. Moreover, the ranging error is within 10−2, and the maximum Doppler frequency error is within 2 Hz.

FH-BOC 신호를 위한 부분 상관을 이용한 비모호 상관함수

Binary offset carrier (BOC) modulation is a method of adding sub-carrier modulation to a signal with binary phase shift keying (BPSK) modulation. Compared to the correlation function of the BPSK-modulated spread signal, the main peak of the BOC signal is sharper. Sharper main peaks, are less affected by the multipath. However, the correlation function of the BOC-modulated spread signal has several side-peaks along with a sharp main peak, which easily causes false-locking during code tracking; this is reffered to as the ambiguity of BOC modulation. A frequency hopping (FH)-BOC modulation scheme is hence proposed to reduce the ambiguity of the BOC signal. However, many false-lock points still appear in the correlation function of the FH-BOC-modulated spread signal. In this study, to reduce the ambiguity of the FH-BOC-modulated spread signal, we propose an unambiguous correlation function using partial correlation. Compared to the FH-BOC-modulated signal, the proposed scheme has almost no false-lock points and is less affected by the multipath. From the simulation results, the highest value of the running average of the multipath error envelope (MEE) of the FH-BOC-modulated signal was about 0.822 m, while the highest value obtained with the proposed scheme under same conditions was about 0.524 m, about 36.2 % lower.

Development of the Digital Health Literacy Instrument: Measuring a Broad Spectrum

The current signal capture algorithm uses the correlation function of the signal to achieve capture, which not only has high processing complexity, but also leads to low synchronous capture accuracy. In order to improve the adaptability of the binary offset carrier signal capture algorithm and to improve the defects of the traditional capture algorithm, the spectrum correction-based binary offset carrier signal capture algorithm will be studied. Based on the established binary offset carrier signal model, the signal tracking capture loop is designed. After the spectral correction processing of the signal, the judgment loop is designed based on the bandwidth folding principle to realize the signal capture. The simulation experiments show that the average capture rate of the studied signal capture algorithm is 95.63%, and the main peak amplitude of the captured signal is higher and the capture effect is better.

Multifunctional Signal Design for Measurement, Navigation and Communication Based on BOC and BPSK Modulation

In a multi-node spacecraft or unmanned aerial vehicle (UAV) group, a multifunctional signal containing measurement, navigation, and communication functions is required to simplify the receiver structure, and to increase spectrum utilization. The paper proposes a multifunctional signal based on a binary offset carrier (BOC) and binary phase shift keying (BPSK) modulation. The signals which carry different functions are orthogonal in the frequency domain, which causes the data transmission signal to not be affected by BOC signal. In addition, in the high carrier to noise ratio (C/N0), the spreading gain of the BOC signal ensures that the communication signal has a slight influence on navigation signals. Moreover, the multifunctional signal can achieve communication and measurement functions at the same frequency point and fast switching in multinodes. These advantages can simplify the receiver design and improve the frequency band utilization. Finally, in this study we completed the design and verification of the hardware system.

Coherent Combining and Long Coherent Integration for BOC Signal Acquisition under Strong Interference

<h3>Abstract</h3> A coherent combining and long coherent integration (CCLCI) scheme is presented for standalone direct acquisition of binary offset carrier (BOC) signals under strong radio frequency interference (RFI). To mitigate the ambiguity of BOC signals, a split-spectrum method extracts the upper and lower sidebands of a BOC signal, treats them separately as two binary phase shift keying (BPSK) signals, and finally combines the results to recover the loss due to splitting. The CCLCI scheme burns through strong interference by building up the desired weak signal while averaging out noise and interference. It exploits all information available (L1 and L2, upper and lower sidebands, odd and even chips, and I- and Q-components) by applying coherent combining across signal components and long coherent integration over time, followed by noncoherent accumulation if necessary. Issues and enabling techniques are described. The results of an embedded implementation in demonstration with a GPS RF simulator are analyzed.

General Design Method for Two-dimensional Multi-correlator Anti-multipath Tracking Loop for BOC Signals

As binary offset carrier (BOC) signals are widely used in global navigation satellite system (GNSS), tracking ambiguity threats and multipath become two main factors which affect ranging precision. Two-dimensional (2-D) tracking loops, such as double estimate tracking (DET) and double phase estimator (DPE), estimate the code delay and subcarrier delay by the delay locked loop (DLL) and the subcarrier locked loop (SLL), respectively, to obtain high precision and unambiguous propagation delay. Although 2-D tracking techniques can effectively alleviate the impact of tracking ambiguity threats, their anti-multipath performance has not been improved compared with one-dimension (1-D) tracking techniques. This paper proposes a general design method for two-dimensional multi-correlator anti-multipath tracking (TMAT) structures based on heuristic optimization. Compared with 2-D tracking loops equipped with traditional anti-multipath structures, such as narrow early minus late (NEML) and double delta (DD) structures, TMAT structures designed for different signals with different bandwidths always have better multipath mitigation performance without any degradation of tracking robustness. According to case studies, because of the great anti-multipath improvement of TMAT structures, the slight degradation in thermal noise performance can be acceptable. Also, the designed TMAT structures are insensitive to relative amplitude of multipath and bandwidth of signals, indicating the great practicality of this technique.

Improved MBOC modulations based on periodic offset subcarrier

With the development of global navigation satellite systems, the modernization of global navigation satellite systems has arrived, which takes the binary offset carrier modulation and related evolution as the typical feature. Moreover, the performance of multiplexed binary offset carrier modulation is related to global navigation satellite systems service. In the paper, an improved multiplexed binary offset carrier modulation based on period offset subcarrier was proposed, called MBOC-POS, where the subcarrier periodic shifting binary offset carrier modulation is used as the lower-order component instead of sine-binary offset carrier modulations. Meanwhile, the different implementations of MBOC-POS modulations are analysed and compared with traditional multiplexed binary offset carrier multiplexed binary offset carrier signals in multipath mitigation, tracking accuracy, anti-interference and compatibility. By simulation and analysis, the performance of reconstructed MBOC-POS modulation has been improved. Especially, for the mismatch reception, the Gabor bandwidth increases by 29.5% and the multipath error envelope is reduced by 35% with the filter bandwidth of 10 MHz. Therefore, the multiplexed binary offset carrier MBOC-POS modulation proposed in the paper can be used as a new option for MBOC modulations and next-generation signal design.

A Low-Processing-Rate Dual BPSK Tracking Method for BOC Modulated Signals

Among the existing wideband processing methods for binary offset carrier (BOC) signals, dual binary phase-shift keying (BPSK) tracking (DBT) features the interoperability with traditional BPSK tracking and flexible switching between single-sideband and wideband tracking modes. However, due to the large bandwidth of entire BOC signal, the DBT method requires a high signal sampling and processing rate, resulting in high computational burden. This letter proposes a low-processing-rate dual BPSK tracking (LPR-DBT) method to tackle this problem. A preprocessing unit is proposed to be added between the ADC and DBT correlator channels under the constraint of retaining the subcarrier ranging information. It converts both the upper and lower sidebands of BOC signal to near-zero frequency, respectively, and then decimates them. This significantly reduces the correlator channel processing rate without ranging performance loss. It is worth emphasizing that the delays and phase shifts introduced by the preprocessing to each sideband are carefully considered and dealt with to ensure the relationship between two sidebands required by the DBT method is not destroyed.

An Unambiguous Synchronization Scheme for GNSS BOC Signals Based on Reconstructed Correlation Function.

Binary offset carrier (BOC) modulation is a new modulation method that has been gradually applied to the Global Satellite Navigation System (GNSS) in recent years. However, due to the multi-peaks in its auto-correlation function (ACF), it will incur a false lock and generate synchronization ambiguous potentially. In this paper, an unambiguous synchronization method based on a reconstructed correlation function is proposed to solve the ambiguity problem. First, through the shape code vector constructed in this paper, the general cross-correlation function (CCF) expression of the BOC modulated signal will be obtained. Based on the features of the signal correlation function, it is decomposed into a matrix form of trigonometric functions. Then, it generates two local signal waves using a specific method, then the proposed method is implemented to obtain a no-side-peak correlation function by reconstructing the cross-correlation between the received signal and the two local signals. Simulations showed that it fully eliminates the side-peak threat and significantly removes the ambiguity during the synchronization of the BOC signals. This paper also gives the improved structure of acquisition and tracking. The detailed theoretical deduction of detection probability and code tracking error is demonstrated, and the corresponding phase discrimination function is given. In terms of de-blurring ability and detection probability performance, the proposed method outperformed other conventional approaches. The tracking performance was superior to the comparison methods and the phase discrimination curve only had a zero-crossing, which successfully removed the false lock points. In addition, in multipath mitigation, it outperformed the ACF of the BOC signal, and performs as well as the autocorrelation side-peak cancellation technique (ASPeCT) for BOC(kn,n) signals.

Optimal Parameter Design of Continuous Phase Modulation for Future GNSS Signals

Continuous phase modulation (CPM) is a power and spectrum efficient modulation that intrinsically possesses constant envelope, phase continuity as well as less out of band (OOB) radiation, especially appropriate for stringently bandwidth-constrained systems employing non-linear power amplifiers. Such advantages render CPM as a promising modulation candidate with application to satellite navigation. CPM comprising of a few parameters has large amounts of modulation subclasses. This paper is devoted to optimal parameter design of CPM for future GNSS signals. Parameter design approaches endowing CPM with similar spectrum profiles as legacy binary offset carrier (BOC) and binary phase shift keying (BPSK) modulations are also proposed. Several optimal subclasses of CPM family are suggested as unimodal or bimodal GNSS signal solutions. The simulation results indicate that the designed CPM signals behave same or similar main lobes with BPSK and BOC signals, and proposed optimal subclasses of CPM family with high spectral efficiency are comparable or superior than legacy modulations, typical GMSK, and filtered multitone (FMT) signal using the squared root raised-cosine (SRRC) basic pulse in terms of tracking accuracy, multipath mitigation and compatibility. In addition, some constructive comments on CPM design are presented, which provides a reference for CPM applications in GNSS.

Theoretical assessment and application of modern GNSS signals acquisition performance

The application of the Global Navigation Satellite System (GNSS) is extensive and has widely infiltrated the national economy and social development in various fields. As critical part of the satellite navigation system design process, GNSS signals performance assessment has received tremendous attention for a long period of time. The mathematical model of GNSS signal detection is built based on single point detection test. An improved acquisition performance assessment method that considers the modulation type, code search step-size, and acquisition algorithms is proposed herein. This study investigates the performance of the overall detection and main/side peak detection for Binary Offset Carrier (BOC), Multiplexed Binary Offset Carrier (MBOC), and Alternative BOC (AltBOC) signals using matched and unambiguous acquisition methods, and obtains quantitative results. With a fixed code search step-size, the multi-peaks of the autocorrelation functions of BOC, MBOC, and AltBOC signals will degrade the acquisition performance. The higher the sub-carrier rate, the more serious is the degradation. Although signal-power loss occurs to some extent, Binary Phase-Shift Keying-like (BPSK-like) and Sub Carrier Phase Cancelation (SCPC) methods significantly improve the acquisition performance.

MBOC(6,1,4/33) 신호의 다중경로 영향 완화를 위한 새로운 Strobe 펄스 설계

In this paper, we propose a novel strobe pulse to mitigate the multipath effect of MBOC (6,1,4/33) signal and analyze its performance. By additionally modulating a passband Direct Sequence/Spread Spectrum (DS/SS) signal with a Binary Offset Carrier (BOC) sub-carrier, the signal band can be moved to a desired band, thereby increasing frequency efficiency. In addition, the correlation characteristics of the correct code synchronization point are improved, so that the multipath effect can be reduced to compare with the existing Binary Phase Shift Keying (BPSK) modulated signal. However, the multipath effect is still one of the major performance limitations of the Global Navigation Satellite Systems (GNSSs). A conventional scheme to mitigate multipath effects of GNSS is the Strobe pulse technique. In this paper, we design a new strobe pulse that can effectively mitigate the multipath effects of MBOC (6,1,4/33) signals, and multipath mitigation in the 2-Ray model, a representative channel environment to assess the multipath mitigation performance by computer-based simulation. In order to compare the performance of the proposed new strobe pulse, the W2 pulse scheme with similar implementation complexity is considered. The W2 pulse technique is the one of the Strobe pulse technique for BOC signal. Based on the output of the discriminator in multipath free environment, the pull-in range of the W2 pulse technique is about 0.2 chips, whereas the proposed scheme is about 0.6 chips, which is about 3 times wider. And the false-lock point of the proposed scheme is less than about 20% to compare the W2 scheme. In the same environment, the multipath error envelope of the W2 and the proposed schemes is shown, and both techniques are affected only by the closed-in multipath signal. Among them, the proposed scheme has significantly lower multipath errors due to the closed-in multipath signal compared to the W2 technique, and the maximum value of the proposed scheme based on the running average of the multipath errors is about 32% compared to the W2 scheme.

Indirect learning Hammerstein HPA predistorter for wideband GNSS signals

Compared with the traditional GPS L1 C/A signal, the existing and emerging new-generation wideband GNSS signals suffer more severe distortions due to the nonlinear characteristics of a high-power amplifier (HPA) in the satellite transmitter. HPA nonlinearity can lead to in-band signal distortion and out-of-band spectral regrowth, which degrade the ranging performance of a GNSS receiver. Researchers have reported power loss, correlation peak asymmetries, lock point bias as well as carrier tracking error caused by the HPA nonlinearity. However, few pre-distortion approaches that compensate for the HPA nonlinear effects have been presented in the GNSS field. We first take BDS-3 B2 asymmetric constant envelope binary offset carrier signal as an example to present the HPA nonlinear effects on wideband GNSS signals. Then, the design principle of a predistorter is investigated, and a Hammerstein predistorter is proposed to eliminate the nonlinear HPA with memory. Finally, we compare the constellation diagram, power spectrum, correlation function, code tracking bias with and without the Hammerstein predistorter. The comparison results demonstrate that a digital predistorter is a potential solution to compensate the HPA nonlinear distortions for wideband GNSS signals. This pre-distortion approach is of great significance that can effectively guarantee the nominal signal quality in space not only during the maintenance of the current GNSSs but also for the future emerging local or global navigation systems.